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Generating Waveforms

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Generating Triangle Waves 

In the basic square wave generator circuit, a graduallycharging capacitor was used to help set the timing or frequency of the circuit. However, since it was only charging through a resistor, it necessarily charged on a logarithmic curve, rather than as a linear ramp. Can we use an op amp integrator here to obtain a linear triangle wave along with the square wave?
In the circuit to the right, we use a separate integrator to generate a ramp voltage from the generated square wave. As a result, we can get both waveforms from a single circuit. The phase relationship shown between the two output waveforms is correct — remember that the integrator inverts as well as integrating, so it will produce a negativegoing ramp for a positive input voltage, and viceversa.
Because we are now using an op amp integrator to get the triangle wave, we no longer have a logarithmic response anywhere in the circuit. Therefore, the equation for the operating frequency is simplified to:
f_{out} =  1  (  R_{2}  ) 
4R_{t}C  R_{1} 
The squarewave amplitude is still the limit of voltage transistion, which we are assuming here to be ±10 volts. The triangle wave's amplitude is set by the ratio of R_{1}/R_{2}. Note that for this circuit to function, it is necessary that R_{1} be less than R_{2}. This keeps the triangle amplitude less than the square wave amplitude. It is also necessary for the resistor values to be within a reasonable range for correct operation of the op amps. There is no restriction on the value of C.


 
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